In carrying out a piping construction for a gas supply, a water supply or an air-conditioner at a wall face, a floor face, a foundation or the like of a building formed by concrete, the wall face or the like is bored by using a concrete drill driven by power of electric power, compressed air or the like. A hole having a predetermined diameter is bored at a concrete wall or the like by a boring blade in a cylindrical shape formed at a front end of a core bit by applying rotation and vibration from a side of a concrete drill to the core bit attached to a chuck portion formed at a front end of the concrete drill. The core bit is formed in a hollow shape, and the boring blade is cooled by supplying cooling water from a side of the concrete drill to the boring blade by way of the hollow inside. Further, a seal is formed between the concrete drill and the core bit, so that the cooling water is not leaked when the core bit is attached.
As described in, for example, JP-A-11-309710 (page 3, FIG. 3), a core bit of a background art comprises a supporting member in a hollow shape having a boring blade at a front end of a drill portion at one end side of the supporting member and having a guide portion in a cylindrical shape at the other end side of the supporting member. The core bit is attached to a concrete drill by inserting the guide portion in the cylindrical shape into a cylindrical inside formed at a chuck portion of the concrete drill. By a contact between an end face of the guide portion in the cylindrical shape of the core bit and a seal member arranged at a deepest portion of a cylindrical portion of the chuck portion of the concrete drill, a center opening of the concrete drill and a center opening of the core bit are connected to seal so that the cooling water is flowed from a side of the concrete drill to a side of the core bit.
Meanwhile, the seal member formed between the core bit and the concrete drill is formed by rubber and therefore, when the seal member is deteriorated by elapse of time and water is leaked by deteriorating a seal function by wear of a surface thereof or the like by frequently using the seal member, the seal member needs to be replaced. However, according to a structure of sealing the core bit and the concrete drill of the background art, the seal member is formed at the deepest portion of the guide portion in the cylindrical shape of the chuck portion of the concrete drill and therefore, there poses a problem that a replacing operation becomes extremely complicated.
Further, when the seal member is formed on the side of the chuck of the concrete drill as in the background art, a durability in conformity with a durability of the concrete drill is required for the seal member, and an expensive material of rubber or the like which is difficult to be deteriorated is used to constitute a factor of increasing cost of the concrete drill.